Re-using air from BCD in dire emergency?

[irishsquid]

... A little tainted air in the lungs is better than water!

CO2 toxicity is gradual. The first symptoms are air hunger and anxiety, and as CO2 builds, you get lethargic and eventually lose consciousness. One of the nasty toxicities of CO2 is acidosis, which builds very quickly and can lead to cardiac arrhythmias. However, if I were 100 feet from the exit to the cave and completely out of gas, I'd try it. I'd try anything; wouldn't you? And if I made it out, I'd sell all my gear because I was clearly much too stupid to continue to dive, for having gotten myself into that bad a situation.

There it is in a nutshell!

 

[SteveAD]

There it is in a nutshell!

Especially the last line about selling gear and quitting diving. There is no excuse for screwing up that bad.

 

[Web Monkey]

I am posting this due to a discussion among scuba friends. The topic was whether it was possible or not, in an emergency situation and without any other source of air use the air which can be found in the BCD more than one time: that is inspire the air, expire back in the BCD and repeat the sequence.

If you're properly weighted and run out of air, your BC will be empty and there won't be anything there to breathe anyway.

Terry

 

[DaleC]

If you're properly weighted and run out of air, your BC will be empty and there won't be anything there to breathe anyway.

Terry

Aha! An excellent but totally obscure reason for using the BC instead of the DS for bouyancy control.

But you raise an interesting point. I'm weighted so that I'm neutral when both tanks reach 500psi. After that I would be fighting positive bouyancy so I wonder if I could go OOA (through neglect) without noticing the bouyancy shift (although I am reminded of that sig that says nothing is impossible for a sufficiently talented fool).

I have tried breathing off the LP inflator before. Just depress both at once and sip off it as you would a freeflowing reg. Probably not going to happen IRL but still good to know how your gear can serve several functions.

I've also contemplated using the BC as an emergency rebreather (when in an OOA situation) but have also heard that air will expand in the tank as you rise and may provide a breath or two so one should keep the reg in the mouth.

My plan is to avoid either scenario like the plague.

 

[IceBergSlim]

......have also heard that air will expand in the tank as you rise and may provide a breath or two .....

That will not happen.

It's a bit of missinformation has been around for a long time.

 

[Gilldiver]

That will not happen.

It's a bit of missinformation has been around for a long time.

The air in the tank will not expand, but depending on your 1st stage you might get a breath on the way up due to changing ambiant pressure changes. Many regs will only give you air out of a tank till the tank pressure is equal to ambiant pressure plus the IP. So, if you drop ambiant pressure, you get a bit more air out of the tanks.

 

[Seadeuce]

CO2 toxicity is gradual. The first symptoms are air hunger and anxiety, and as CO2 builds, you get lethargic and eventually lose consciousness.

Just to clarify here - if you are at depth then CO2 toxicity can hit you quickly if your breathing is shallow due to exertion. IOW you are not exhaling deeply enough.
Having had that experience (due to a downcurrent) I can vouch for the symptoms - overwhelming tiredness in one moment, next step to unconsciousness. Only remedy is to ascend and decrease the PP of the gas in your system.

Toxicity would be gradual in the situation described, i.e. breathing from the BC. But if you do it at depth then the effects are greatly enhanced.

I would imagine many "unexplained" diving deaths, with air left in their tanks, have been due to CO2 blackout.

Apologies for the mid-thread interruption!


Seadeuce

 

[The Kraken]

It would be interesting to conduct an exercise in breathing from a B/C from 100' in a controled experiment.

the K

 

[Web Monkey]

But you raise an interesting point. I'm weighted so that I'm neutral when both tanks reach 500psi. After that I would be fighting positive bouyancy so I wonder if I could go OOA (through neglect) without noticing the bouyancy shift (although I am reminded of that sig that says nothing is impossible for a sufficiently talented fool).

It is a rather interesting "safety feature".

If you're properly weighted, by the time you're OOA, you'll be about 1 Lb positive if diving an 80 cubic foot tank, although that's not much weight and is probably offset by wetsuit compression at depth.

Terry

 

[Web Monkey]

It would be interesting to conduct an exercise in breathing from a B/C from 100' in a controled experiment.

Let us know how that goes for you . . .

Terry